Secondary batteries such as lithium ion secondary batteries, nickel hydride batteries and the like have been gaining in importance in recent years as power sources installed in vehicles, or power sources in personal computers and mobile terminals. In particular, lithium ion secondary batteries, which are lightweight and afford high energy densities, are preferably used as high-output power sources installed in vehicles. In one typical configuration, such lithium ion secondary batteries are provided with a positive electrode that is formed from a lithium transition metal complex oxide, a negative electrode that is formed from a carbon material, and a separator that is disposed between the positive electrode and the negative electrode. Patent Literature 1 and Patent Literature 2 illustrate instances of conventional technologies pertaining to such separators. Patent Literature 1 discloses a separator wherein a microporous material made of a polyolefin resin is provided inside a nonwoven fabric made of glass fibers, and on at least one surface of the nonwoven fabric.
Patent Literature 2 discloses a separator formed of a microporous resin film in which insulating glass fibers or aramid fibers are dispersed in a polyolefin resin.